1. Field of the Invention
This invention relates to an arrangement for limiting the pressure developed within a closed container and, more particularly, for limiting the pressure developed by a potentially explosive gaseous mixture in rechargeable batteries.
2. Description of the Prior Art
When a device such as a battery containing a plurality of electrochemical cells within a closed container is charged or discharged, hydrogen and oxygen gases are generated by the decomposition of the electrolyte of the cells and accumulate in the battery. Since the hydrogen and oxygen are within a closed space, there is always the possibility of the development of excessive pressure caused by the combination of the hydrogen and oxygen. The combination of these gases results in a sudden pressure rise that can burst the container enclosing the cells as well as damage surrounding equipment and be hazardous to personnel. This problem exists not only with respect to sealed containers for batteries but also in vented containers because the pressure relief vents may be inadequate for relieving such excessive pressure build-up. The problem can also be encountered in a system containing purging means to prevent accumulation of explosive gases, where the purging means fails to purge the container adequately. The problem is also encountered in environments other than batteries where potentially explosive gaseous mixtures may accumulate in a confined space.
One solution for reducing the hazards of gases in a battery includes the provision of a stronger container having the capacity to withstand such sudden increases in pressure. However, such a container would add considerable expense and weight to the device. It has also been proposed to increase the flexibility of the container walls so that they may expand, thus increasing the container volume to accommodate for the pressure build-up. However, it would be desirable to contain the resulting gases with little or no change in the shape and size of the container, particularly the container of a battery for an automobile or aircraft, for example, wherein there is limited space to accommodate the battery.
Another prior art solution includes the use of activated charcoal to absorb gas. The activated charcoal is not effective, however, where space and weight constraints must be taken into account because of the large quantity of charcoal required to absorb evolved gas.
Still another prior art solution includes the reaction of oxygen with the hydrogen gas in the presence of a palladium catalyst to form water. The reaction of oxygen with the hydrogen gas in the presence of the palladium catalyst has proven to be unreliable because of the poisoning of the palladium by the reaction. A further refinement of this prior art solution is to use palladium oxide as a catalyst in lieu of the palladium since only a small quantity of palladium oxide is required and the palladium oxide is not poisoned by the reaction. Although the palladium oxide limits pressure build-up, the hazard caused by the evolution of hydrogen gas is not entirely eliminated, and the evolved hydrogen in the presence of oxygen may still represent a mixture which is capable, upon combination, of generating pressures many times greater than the original ambient pressure.
By this invention, the disadvantages and limitations of the prior art are overcome, and an arrangement is provided for limiting the pressure increases developed by the combination of gases of a gaseous mixture to a level which eliminates the possibility of rupture of the container enclosing the gaseous mixture.
Accordingly, it is an object of this invention to provide an arrangement for limiting the pressure generated within a closed container, such as a battery, by the combination of gases formed therein to a level below that causing rupture of the container.
It is another object of this invention to provide an arrangement for limiting pressure increases within a container without substantially increasing the weight of the container.
It is still another object of this invention to provide an arrangement for limiting pressure increases within a container to prevent damage to the contents of the container as well as the external surroundings of the container.